1. Field of the Invention
The present invention relates to an electronic circuit, a protective device, and an image forming apparatus.
2. Description of the Related Art
A circuit including a Zener diode is known as a protective circuit against overvoltages.
Japanese Unexamined Patent Application Publication No. 2009-177865 discloses a protective circuit that includes a Zener diode and a field effect transistor (FET). In the protective circuit disclosed in Japanese Unexamined Patent Application Publication No. 2009-177865, current flows also through the FET when the Zener diode breaks down.
When a device to be protected outputs a large current, the protective circuit needs to include a Zener diode having a large allowable dissipation. Zener diodes having a large allowable dissipation, however, cost high.
Even in a configuration including a plurality of Zener diodes connected in parallel with each other, only one of the Zener diodes breaks down due to variations involved in a breakdown voltage (Zener voltage). Thus, the connection of Zener diodes in parallel with each other does not increase the allowable dissipation, disabling the protective circuit to pass a large current.